REPORT

OF THE COMMITTEE

ON

IDENTIFICATION OF THE AREAS OF

RESEARCH IN FOREST HYDROLOGY

AND

SUGGESTED MEASURES

TO ACHIEVE THE RESEARCH MANDATE

November, 2011

i

EXECUTIVE SUMMARY

Forests are dynamic ecosystems subject to both incremental and episodic disturbances

that vary in frequency, severity, and extent. The forests are managed for a number of

purposes—timber harvesting, wilderness, habitat, and recreation—but arguably their most

important output is water. Precipitation is cycled through forests and soil, and ultimately

some is delivered as stream-flow to receiving bodies of water. The current knowledge in

forest hydrology science provides the general magnitudes and directions of direct hydrologic

responses to changes in forests over short time scales and in small areas. However, today’s

forest and water managers need forest hydrology science to predict or indicate the hydrologic

responses in forest landscapes that are changing over large areas or long time scales.

Predictions are needed to understand the indirect and interacting hydrologic responses to

changes in forested landscapes associated with climate change, forest disturbances, forest

species composition and structure, and land development and ownership, and how these

changes will affect water quantity and quality downstream and over long time scales. A

sound knowledge base supported by the findings of research studies in the area of forest

hydrology science would help support forest and water management decisions in many ways.

Considerable progress has been made in forest hydrological research all over the

world. However, studies in India on forest hydrology have been done on a modest scale, and

largely limited to small watershed scales only. The initial studies focused on the hydrologic

effects of forest degradation. Recently, the research has shifted to studying reforestation

hydrology, large-scale watershed hydrology, climate change impacts, and application of

hydrological models. But, the forest hydrology in India is still in an infant stage because most

of the studies conducted are in the scattered form. The information to define the entire

hydrological system and water budget of a particular forest type is not yet available. Further,

most of the studies have been conducted at plot or small watershed scale with study period

ranging from a single storm event to a few years.

The present report is an outcome of the committee constituted by the Director

General, Indian Council of Forestry Research and Education (ICFRE) ) to identify the areas

of research and suggest measures to achieve the mandate on Forest Hydrology as a

component under All India Coordinated Research work on Climate Change. The report is

ii

divided into seven chapters. The first Chapter gives a brief background for preparing the

report, the details of the committee and the meetings held by the committee to deliberate on

research areas in forest hydrology. The second Chapter on ‘Forest and Water’ reviews the

general understanding of how forests and their dynamic nature affect various hydrological

processes within the catchments and the catchment output in terms of water quantity and

quality. Since forests serve as an important means to capture and store atmospheric carbon

dioxide in vegetation, soils and biomass products, the aspects related to carbon sequestration

in forested soils are discussed in Chapter 3. A brief review of forest hydrology science in

India and the emerging research issues are presented in Chapter 4. Considering the current

status of forest hydrology in India, a number of actions are suggested and potential research

areas are identified in Chapter 5. The suggested actions that could help address key questions

about the long-term hydrologic effects of forest change and conversions include (i)

compilation of status of research on forest hydrology (ii) preparation of a catalogue of

historical & modern hydrologic records, and (iii) continuing current small watershed

experiments and re-establishing small watershed experiments where research has been

discontinued. The research studies identified in the report need to be carried out through a

chain of interlinked long-term projects using paired watershed approach in different geo-

ecological conditions. The nested approach on sub-watershed basis within selected

watersheds is suggested for long term hydrological measurement using an integrated

approach of hydrologic instrumentation, field investigation, remote sensing and GIS

techniques. The reminiscent measures to implement the proposed research studies are

presented in Chapter 6. It is suggested that a separate Division of Forest Hydrology may be

established at ICFRE, Dehradun to provide an impetus to the much needed research work in

the area of forest hydrology. Concerted and joint efforts are also needed by the scientists from

premier research institutes working in the area of hydrology and forestry to take up the

sponsored research projects in the area of forest hydrology. An All India Coordinated

Research Project is suggested for carrying out various research studies suggested in the

report. The project is suggested to be implemented jointly by NIH, ICFRE and CSWCRTI in

a collaborative project mode as these organizations have their research centres / institutes

across the country. Finally, the need for capacity building in the area of forest hydrology is

emphasized in Chapter 7.

iii

CONTENTS

S. NO. TITLE PAGE NO.

EXECUTIVE SUMMARY i

CONTENTS iii

1. BACKGROUND 1

2. FORESTS AND WATER 2

2.1 Natural Forest Modifiers and Forest Management Practices 2

2.2 Hydrologic Effects of Forests Disturbances and Management Practices 4

2.2.1 Changes in Interception and Evapotranspiration 4

2.2.2 Changes in Infiltration and overland flow 5

2.2.3 Changes in Soil Properties and Soil Moisture Storage 5

2.2.4 Changes in Watershed Outputs 6

2.2.4.1 Changes in water yield, peak flows and low flows 6

2.2.4.2 Changes in water quality 7

3. CARBON SEQUESTRATION IN FORESTED SOILS 8

4. FOREST HYDROLOGY SCIENCE IN INDIA AND EMERGING ISSUES 10

4.1 Forest Hydrology Science in India 10

4.2 Emerging Issues in Forest Hydrology 11

4.3 Research Needs 11

4.3.1 Cumulative Watershed Effects 11

4.3.2 Climate Change 12

4.3.3 Forest Management 12

5. SUGGESTED FUTURE ACTIONS AND AREAS OF RESEARCH 13

5.1 Suggested Future Actions 13

5.2 Suggested Future Areas of Research 13

6. SUGGESTED ROAD MAP 15

6.1 Recommendations 15

7. CAPACITY BUILDING IN THE AREA OF FOREST HYDROLOGY 18

REFERENCES 20

ACKNOWLEDGEMENTS 24

APPENDICES 1 – 5 25-31

ANNEXURES 1 - 4 32-62

1

1. BACKGROUND

A committee was constituted by the Director General, Indian Council of Forestry

Research and Education (ICFRE) vide Office order no. 31-19/2001-ICFRE dated 8th

July,

2011 (Appendix 1) to identify the areas of research and suggest measures to achieve the

mandate on Forest Hydrology as a component under All India Coordinated Research work on

Climate Change. The committee held its first meeting on 11th

August, 2011 in New Delhi and

deliberated on various research issues in the area of forest hydrology and also on the action

plan for preparation of the report. Dr. Jaivir Tyagi, Scientist ‘F’ was nominated as Member-

Secretary of the committee and was entrusted with the work of preparation of the draft report

based on the inputs received from other members of the committee. Based on the

recommendations of the committee members in the meeting, two more members were also

included in the above committee. The modified constitution of the committee and the minutes

of the first meeting are given in Appendix 2 and 3 respectively.

In partial modification of the above said office order, the Director General, ICFRE

further expanded the committee vide office order no. 31-19/2001-ICFRE dated 26th

Sept.

2011 (Appendix 4). The second and final meetings of the committee were held on 13th

and

14th

October, 2011 respectively at FRI, Dehradun. The list of members who attended these

meetings is given in Appendix 5.

The present report is being presented based on the deliberations by the committee

members during these meetings. The information and suggestions received from various

committee members have been duly incorporated in the report.

2

2. FORESTS AND WATER

Forested areas often constitute head water catchments for many large rivers. However,

forests vary due to differences in geography; ecology; and social, economic, and land use

histories. These are also managed for a range of objectives and goals, using a wide variety of

forest management practices that tend to change the forest composition and structure. There

is now a broad scientific agreement that type of forests and their management practices have

the potential to alter the quantity, quality and timing of water moving through catchments by

altering the interception, evapotranspiration, soil infiltration, nutrient and sediment load of

runoff etc. (Anderson et al., 1976; Ice and Stednick, 2004). Further, there is a prevalent

assumption that there exists a positive correlation between forested lands and water flows

which is reflected both in the national forest and water policies and in the implementation of

watershed development programs in India. However, scientific studies from various parts of

the globe have also shown that this is not a universal truth and that there are situations where

the general perceptions regarding the forest-water interface are not supported by empirical

findings. In fact, the findings forewarn against adverse impacts in the long run and emphasize

the necessity for a scientifically-informed approach to forests and water management

programs. In recent years, concern has also grown of the potentially large but uncertain

effects of climate change on forests and their water output. Climate change may cause shift in

snow line, increased favourable conditions for forest fires, outbreaks of insects and disease,

and changes in forest structure and species composition, producing direct hydrologic effects.

2.1 Natural Forest Modifiers and Forest Management Practices

Forests are dynamic systems which can be modified by (1) natural disturbances, and

(2) forest management practices. The natural disturbances generally include (a) wildfire (b)

species changes, and (c) insects and disease. The management practices may include (a)

forest harvest and silvicultural activities (b) construction of roads and trails, and (c) grazing

(Fig. 1). Historically, many forest management practices have centred on timber

management. Timber management encompasses silvicultural treatments to establish and

sustain wood production; protection against or control of wildfire occurrences, insect

infestations, and diseases; and of course, harvesting of merchantable trees in a forest (NRC,

2008). Silvicultural practices include selection of species and genotypes, site preparation,

3

planting, drainage, fertilization, watering, herbicide application, and thinning to maximize the

growth of the most desirable species. Forest protection practices include fuel reduction

treatments such as over-story thinning, understory removal, or prescribed fire; construction of

fire breaks and fire lines; applications of soil, water, or fire-retardant chemicals; application

of insecticides and fungicides; and introduction of biological control agents. Timber harvest

practices include selection of rotation age, which determines the ranges of forest ages; road

and path construction, including road drainage systems such as culverts; felling and skidding

of logs to landings; and movement of logs, usually by trucks, to timber mills for processing.

Fig. 1: Schematic diagram of the hydrologic response to forest modifiers

and forest management practices (Source: NRC, 2008)

4

2.2 Hydrologic Effects of Forests Disturbances and Management Practices

Forest disturbances and management activities involve a number of actions which

cause changes in the forest structure, flow paths of water in soil and sub-soil, and the water

and soil chemistry within the forest system that individually and cumulatively can modify the

watershed output in terms of water quantity, quality, and timing. The science of forest

hydrology has built a foundation of general principles that elucidate direct effects of forest

management and disturbance on hydrology. The principles are derived from plot studies,

process studies and watershed experiments. These principles are briefly discussed below.

2.2.1 Changes in Interception and Evapotranspiration

During a precipitation event, much of the rainwater or snow is temporally held on

leaves, plant stems, ground flora and leaf litter. The temporary storage slows down the rate at

which precipitation arrives at the forest floor. If this captured moisture evaporates, it

effectively decreases the amount of precipitation. Reduction in leaf area and other

intercepting surfaces due to fire, trees harvest, insects, disease, forest types and forest age

results in reduced interception loss and therefore increased amount of water reaches the

mineral soil (Verry, 1976), which is available for soil moisture storage, transpiration, or

runoff (Helvey, 1971). Where forest canopies capture additional moisture from clouds, a

reduction in leaf area can decrease net precipitation (Harr, 1982; Hutley et al., 1997).

The process of evapotranspiration in forests accounts for considerable loss of gross

precipitation. A reduction in leaf area reduces evapotranspiration and increases water

available for runoff. The magnitude and persistence of the reduction in transpiration depends

on the amount and type of the vegetative canopy removed and the rate at which the vegetative

cover is re-established. A reduction in leaf area also increases the amount of light reaching

the forest floor, increasing energy exchange between soil or snow and the atmosphere and

altering the energy budget. Increased exposure of snowpack to solar radiation and to turbulent

heat transfer by wind leads to increased snowmelt rates and earlier onset of snowmelt relative

to undisturbed forest canopies (Hornbeck et al., 1997; Jones and Post, 2004).

5

2.2.2 Changes in Infiltration and Overland Flow

Layer of organic material, surface obstacles, root system and activities of micro-

organisms facilitates higher infiltration rates in forest soils than other land uses (Mohan and

Gupta, 1983). Most of the soil surfaces under dense forest environment facilitate complete

infiltration of rainwater from light to moderate intensity rains. In most cases this water moves

by subsurface pathways to the stream. Because of high infiltration rates in forest soils, little

water flows over the ground surface as infiltration excess.

Forest management activities and forest disturbances may remove or alter the surface

layers of forest soils, and thereby reduce infiltration and increase overland flow. When

organic surface layers are removed or burned, underlying mineral soil is exposed to raindrop

splash and fine soil particles can accumulate on surface, reducing infiltration and increasing

overland flow. Forest management activities and disturbances also create impervious surfaces

(e.g., roads and trails) and modify hill-slope in ways that alter water flow paths in soils and

sub-soils, shift subsurface flow to surface flow, and increase runoff and erosion rates. If soils

are compacted to the extent that infiltration rates are lower than rainfall or snowmelt rates, the

resulting overland flow can greatly increase runoff rates and surface erosion.

2.2.3 Changes in Soil Properties and Soil Moisture Storage

Forests alter the bulk density, porosity, structure and water holding capacity of the

soil and these properties are responsible for retention and mobility of water and nutrients;

habitat for micro and macro fauna. The additional soil water storage potential in forested soils

is possibly due to (i) high organic matter content (ii) dense tree roots system and (iii) high

soil organic carbon content. The organic matter and the root system improve the soil

structure, increase the infiltration of water and water holding capacity of the soil (Marshall

and Holmes, 1988; Kang et al., 1996; Jiang, 1997; Teresaecheverria and Martinez, 2001).

The higher percentage of soil organic carbon improves the overall soil environment and the

water holding capacity (Bhattacharyya et al., 2007). Jones (2006) reported an additional

water holding capacity of 144,000 litres per ha per percentage of soil organic carbon. Tyagi et

al. (2011) reported higher soil moisture storage under dense sal forest that that under open sal

forest. It is also reported in the literature that root system of an oak tree is very extensive and

soil-root complex system of each mature oak tree has a capacity to store several hundred

litres of water, which is released as base flow during the lean season.

6

2.2.4 Changes in Watershed Outputs

2.2.4.1 Changes in water yield, peak flows and low flows

Removal of forests due to forest fires or cutting of trees increases water yield because

of reduced interception and transpiration losses (Bosch and Hewlett, 1982; Jones and Post,

2004; Brown et al., 2005). The increase in water yield varies with factors such as climate,

seasonal timing of precipitation, amount of forest removed, storage of water in soil and snow,

type and age of forest removed, and time since harvest. In regions of low rainfall and high

evapotranspiration, the increase in water yield is largely offset by increased soil evaporation

and evapotranspiration by any remaining vegetation. As forests regenerate after harvest,

water yield increases disappear. The water yield increases have been found to persist ranging

from a decade in some areas to multiple decades in other areas depending on the type of the

forest, soils, climate, reforestation methods, and harvest treatments (Bosch and Hewlett,

1982; Troendle and King, 1985; Hornbeck et al., 1997; Jones and Post, 2004; Brown et al.,

2005). Forest roads and trails also increase overland flow because of their compacted soil

surfaces with very low infiltration rates. Roads constructed on steep slopes intercept water

flowing in the subsurface and further increases overland flow (Megahan, 1972; Wemple and

Jones, 2003).

Recent compilations of studies show wide variability in the magnitude of peak flow

response to forest harvest (Grant et al., 2008). Much of this variation is attributed to the

factors like event size, type of precipitation, proportion of area harvested, topographic relief

and elevations, and time since harvest. In many cases, the absolute increase in peak flows was

larger with larger storms. In rain events, forest harvest affects peak flows directly through

changes in soil water. In events involving snow, the effect of forest harvest on peak flows

depends on how forest harvest changes snowpack size and snowmelt, as well as soil moisture.

Peak flow increases have been detected after only 25 percent harvest of a small watershed

(Harr et al., 1979; Jones and Grant, 1996). As forests regenerate, peak flows return to pre-

harvest levels (Troendle and King, 1985; Jones, 2000). Roads redistribute water locally and

alter flow routing. They contribute to an increase in the size of peak flows by increasing the

amount of surface runoff from impervious surfaces, intercepting subsurface storm flow, and

speeding the delivery of this runoff to the stream network through ditches or gullies

(Megahan, 1972; Wemple and Jones, 2003).

7

Relative to peak flows or annual water yields, few studies have examined the effects

of forest harvest on low flows. Most studies show an initial increase in low flows

immediately after forest harvest but these are often short-lived due to the relatively rapid

recovery of leaf area, interception capacity, and transpiration rates. The increase in low flows

often is followed by a decrease in low flows to below pre-harvest levels (Hicks et al., 1991;

Hornbeck et al., 1997; Swank et al., 2001). These decreases occur when a forest with

relatively high transpiration and/or interception replaces a forest with relatively low

transpiration or interception, such as during species conversion (e.g., deciduous to evergreen)

(Swank and Crossley, 1988); or regeneration of a young stand with higher water use than the

mature stand it replaces (Hicks et al., 1991; Perry, 2007). Because relatively few studies have

examined long-term trends in low flows, there is much uncertainty about this subject.

2.2.4.2 Changes in water quality

Many studies have shown that timber harvest practices greatly increase surface

erosion (Dunne and Leopold, 1978). Overland flow and surface erosion are very low in

undisturbed forests, but logging operations expose surface soils and lead to surface erosion.

After forest harvest on steep slopes, decreased root strength, increased soil moisture and pore

water pressures result in reduced soil cohesion and contribute to decreased slope stability and

increased likelihood of landslides during precipitation events. Forest clear cutting may

increase the landslide erosion rate by two to nine times relative to undisturbed areas (Sidle

and Ochiai, 2006; Miller and Burnett, 2007). High rates of overland flow along unpaved road

surfaces entrain sediment, erode road surfaces, and contribute fine sediment to forest streams

(Reid and Dunne, 1984).

After forest fires, ash deposition can increase pH of surface water and soil. Transient

pH values of 9.5 were measured in streams after a fire in eastern Washington (Tiedemann et

al., 1979). Fire can cause a short-term increase in stream nitrate concentrations, and the

delivery of ash and fine sediment can increase phosphorus concentrations in streams. During

forest fires, chemical fire retardants are applied aerially to forests. Recent studies have shown

that the effects of these chemicals on water quality may persist for years after application

(Morgenstern, 2006). Fire retardants can contain nitrate and possibly sulphate, phosphate, and

some trace elements. When these materials enter rivers, streams, and lakes, they react with

sunlight to form compounds that are toxic to aquatic organisms.

8

3. CARBON SEQUESTRATION IN FORESTED SOILS

There is a growing international concern over the accumulation of greenhouse gases

in the earth’s atmosphere. Carbon dioxide (CO2) is one of the major greenhouse gases and it

has increased significantly in recent decades. Concentration of atmospheric CO2 can be

lowered either by reducing emissions or by taking CO2 out from the atmosphere and stored in

the terrestrial, oceanic or aquatic ecosystems.

Soil has a vicious relationship with vegetation. The accumulation of soil organic

matter under trees is the most commonly reported effect of trees on soils. Tree growth serves

as an important means to capture and store atmospheric carbon dioxide in vegetation, soils

and biomass products (Makundi and Sathaye, 2004). After the litter fall, the detritus is

decomposed and forms soil organic carbon by microbial process. This sequestered carbon

finally act as sinks in the forest land. Soil Carbon has much longer residence mean times than

the Carbon in the vegetation that the soils support. Soils provide a significant reservoir for

organic carbon, storing twice as much as the atmosphere and three times as much as plants.

On comparing the carbon storage in top 1 foot of soil under six land uses, it was found that

forests had the best mitigation potential followed by agro-forestry, plantations, agriculture

etc. (Jha et. al., 2001). Soil Organic Carbon (SOC) has been ignored because it was treated as

a dead biomass. After the awareness of climate change its importance has been recognized

worldwide. Changes in forest type, productivity, decay rates and disturbances can effectively

modify the carbon contents of forest soils. Land use and soil management practices can

significantly influence soil organic carbon dynamics and carbon flux of the soil (Batjes, 1996;

Tian et al., 2002). Input of organic matter is largely from above ground litter, therefore, forest

soil organic matter tend to concentrate in upper soil horizons. This layer is readily depleted

by anthropogenic disturbances such as land use changes and cultivation. Forest fire,

overgrazing, etc. lead to the soil degradation and loss of soil organic matter store.

Deforestation is one of the most important sources of CO2 emission in to the atmosphere.

From hydrologic point of view, the SOC also plays a key role in improving the physical

properties of soil, which are responsible for infiltration, percolation, permeability, and

hydraulic conductivity of land.

9

The variety of soils occurring in India offers different potential for carbon

sequestration. They also need different sets of strategic management for improving their

mitigation potential because of their different mineralogical, biophysical and chemical

behaviour and response to a given input (Negi and Gupta, 2010). There is a need to

formulate a strategy for more precise SOC estimation and monitoring thereafter under

different forest covers, land uses and also under the Trees Outside Forest (TOF). Major

considerations for soil management are to develop knowledge bank on geological/

mineralogical, physical, chemical, biological and microbiological properties and the inter-

linkages. The regional specificity of soil behavior could then be understood and managed for

finally stabilizing GHGs nationwide on a sustained basis.

10

4. FOREST HYDROLOGY SCIENCE IN INDIA

AND EMERGING ISSUES

4.1 Forest Hydrology Science in India

Forest hydrology draws from the sciences of hydrology and forestry to address

primary questions about forests and water: What are the flow paths and storage reservoirs of

water in forests and forest watersheds; how do modifications of forests influence water flow

paths and storage; and how do changes in forests affect water quantity and quality? The

science of forest hydrology helps to understand the changes that occur in catchment water

balance and stream flows resulting from many interacting factors within forest systems

including climate change, forest disturbances, forest species composition and structure, and

forests defragmentation.

Researchers seeking to answer these kinds of questions have obtained most of their

data from what are known as “paired watershed” studies. Using this approach, two

watersheds that are similar in size, initial land use or land cover, and other attributes are

selected for study. Both are monitored, and while one is left as a “control,” the other is

“treated” (subjected to manipulations such as forest cutting, road building, fires, and so on).

The measured changes in the stream flow and water quality between the two watersheds

quantify the effects of forest treatment and growth. Paired watershed studies, along with

process measurements, plot-scale studies, and hydrologic modelling are important elements

of forest hydrology. However, plot studies and paired watershed studies have generally been

conducted in small, homogenous, areas and over short time spans, ranging in size from less

than a square meter to few km2 and typically spanning only a few growing seasons.

Considerable progress has been made in forest hydrological research all over the

world. However, studies in India on forest hydrology have been done on a modest scale, and

largely limited to small watershed scales only. The initial studies focused on the hydrologic

effects of forest degradation. Recently, the research has shifted to studying reforestation

hydrology, large-scale watershed hydrology, climate change impacts, and application of

hydrological models. But, the forest hydrology in India is still in an infant stage because most

of the studies conducted are in the scattered form. The information to define the entire

hydrological system and water budget of a particular forest type is not yet available. Further,

11

most of the studies have been conducted at plot or small watershed scale with study period

ranging from a single storm event to a few years.

4.2 Emerging Issues in Forest Hydrology

Undoubtly, the micro-watershed based research has proved very useful in studying the

influence of forests on various hydrological processes and in understanding the hydrological

behaviour at micro level. However, forests are now being affected by many interacting

factors, including climate change, forest disturbances, forest species composition and

structure, and land development and ownership, which can break up forests into smaller, non-

contiguous parts. Today’s forest and water managers need forest hydrology science that helps

them understand and predict how such factors will affect water quantity and quality across

large areas and over long time scales. The key unresolved issue in forest hydrology is how to

scale up findings that were developed in small, homogeneous watersheds to predict long term

hydrologic responses across large, heterogeneous watersheds and landscapes. A landscape

perspective allows analysis of forest and water connections over larger areas so as to be able

to use the general principles of forest hydrology to make predictions about forests and water

that can address current and anticipated future issues, including cumulative watershed effects,

climate change, and forest management practices in the 21st century.

4.3 Research Needs

The future research should focus on following aspects for quantitative

characterization of hydrologic variables at different temporal and spatial scales.

4.3.1 Cumulative Watershed Effects

Cumulative watershed effects are the hydrologic effects resulting from multiple land

use activities over time within a watershed. Extreme precipitation events often reveal

cumulative watershed effects and spur public interest in better understanding how land uses

in forested headwaters are related to downstream flooding and other effects. Assessing

cumulative watershed effects requires an understanding of the physical, chemical, and

biological process that route water, sediment, nutrients, pollutants, and other materials from

slopes and headwater streams to downstream areas. Future research in this area should strive

to elucidate the relationships among forests, water flow paths and quality, and watershed land

12

use over large spatial and long temporal scales. This can be achieved through hydrological

modelling.

4.3.2 Climate Change

The effect of climate change on forests and water is increasingly evident, and future

aspects of climate change are likely to have major effects on forest hydrology. Direct effects

of climate warming on forests and hydrology are being observed, such as changes in the

timing of snowmelt runoff and increases in wildfires, but more research is needed to better

predict indirect effects of climate change, including evaluations of how changes in forests and

forest management influence hydrologic response.

4.3.3 Forest Management

Forest management practices evolve over time. The forces that modify forests today

are triggering forest managers to institute novel and contemporary forest management

practices. These new practices such as thinning for fuel reduction and best management

practices have not yet been assessed for their hydrologic effects. Hydrologic effects of these

contemporary management practices need to be understood over long temporal and large

spatial scales.

13

5. SUGGESTED FUTURE ACTIONS AND AREAS OF RESEARCH

In view of the discussion in the preceding chapters, a chain of actions and interlinked

long-term projects need to be carried out in the area of forest hydrology. These are

summarised below.

5.1 Suggested Future Actions

The following actions are suggested that could help address key questions about the

long-term hydrologic effects of forest change and conversions.

1. Compilation of status of research on forest hydrology incorporating the thorough and

critical review of the works done in the area of Forest Hydrology in India and abroad

including references (published and unpublished literature both).

2. Preparation of a catalogue of historical & modern hydrologic records.

3. Continuing current small watershed experiments and re-establishing small watershed

experiments where research has been discontinued.

5.2 Suggested Future Areas of Research

1. Selection of paired representative watersheds (two watersheds similar in size, initial

land cover & other attributes) in different geo-ecological conditions for long term

hydrological measurement using an integrated approach of hydrologic

instrumentation, field investigation, remote sensing and GIS techniques. One

watershed may be kept as control while other may be treated subject to manipulations

such as change in forest cover and forest management practices.

The rainfall, runoff and soil loss from forests of various composition

representing different agro ecological regions of the country on watersheds basis (500

to 10,000 ha consisting of homogenous land use) is rarely available. It is therefore

recommended that a nested approach may be adopted within the paired watersheds for

extensive gauging on sub-watershed basis consisting of homogeneous forest land use

and ranging in size from micro (about 500 ha) to macro-watersheds (about 10,000 ha).

14

2. Hydrological investigations on the effects of different tree species and forest types on

interception, infiltration, soil moisture, ET, water yield and groundwater in

representative watersheds.

3. Investigations on changes in soil physical properties, moisture holding capacity of

soils and carbon sequestration under different forest species.

4. Effect of different forest management practices and forest defragmentation resulting

from social changes on water yield, flood peaks, regulation of stream flows, sediment

yield, water quality, etc.

5. Monitoring of spring discharge which represents the groundwater in the forested

mountainous watersheds.

6. Monitoring water quality parameters of streams and springs in the selected

representative watersheds

7. Effect of global warming and climate change on migration of forest types with respect

to altitude, changes in structure and composition of forests; and the effects thereof on

hydrological parameters including ET & runoff

8. Use of long term observed data for development and application of physically based

distributed hydrological models to predict the impacts of changes in forests on large

and un-gauged basins.

Water is the most important resource among different ecosystem services from a

forest watershed and plays an important role in the survival and livelihood of local people.

Social milieu of local communities is intertwined with water related traditions, ITKs, myths

and so on. Hence, water related social aspects must also find their due place in any research

project on forest hydrology.

15

6. SUGGESTED ROAD MAP

The advancement of the forest hydrology science encompasses a chain of interlinked

projects to study the relationship amongst various vegetative & hydrological parameters and

to assess the cumulative effect of these interactions in terms of water output using

hydrological modelling approach. As such, these studies require long-term field

measurements of vegetation and hydrologic variables using an integrated approach of

hydrologic instrumentation, field investigation, remote sensing and GIS techniques.

Therefore, concerted and joint efforts are required by teams of scientists and professionals

from various disciplines including hydrology and forestry.

6.1 Recommendations

(i) Indian Council of Forestry Research and Education (ICFRE), an apex body in the

national forestry research system, needs to strengthen its capabilities for conducting

hydrological research studies in forested areas. It is recommended that a separate Division of

Forest Hydrology may be established at ICFRE to provide an impetus to the much needed

research work in the area of forest hydrology. For this purpose, the scientific expertise may

be pooled from the existing resources at the ICFRE. Alternatively, the scientists may be

deployed through direct recruitment at junior level and on deputation basis at senior level.

(ii) The studies identified in the report need to be initiated in different geo-ecological

regions in long-term projects mode. The following premier research institutes in the area of

hydrology and forestry which have their research centers across various regions of the

country (Fig. 2) may take up the research projects either in sponsored project mode or

consultancy mode.

National Institute of Hydrology (NIH), an autonomous body under Ministry of Water

Resources, Govt. of India, is a premier research institute in the area of hydrology. The

Institute with its headquarters at Roorkee (Uttarakhand) was established with the main

objective of undertaking, aiding, promoting and coordinating systematic and scientific work

in all aspects of hydrology. The Institute also has six Regional Centres located at Jammu

(J&K), Sagar (M.P.), Patna (Bihar), Guwahati (Assam), Belgaum (Karnataka) and Kakinada

(A.P.). The Institute is well equipped to carry out computer, laboratory & field oriented

16

studies. The Institute has a team of highly qualified and dedicated scientists engaged in

carrying out field and computer based research studies in various disciplines of hydrology

and water resources. The NIH has carried out a number of studies in the area of forest

hydrology in recent past either independently and in collaboration with State Governments /

other organisations. Currently, a project on forest hydrology is being carried out in

collaboration with FRI, Dehradun.

Fig. 2: Locations of NIH, ICFRE and CSWCRTI and their regional Centres / Institutes

HFRI, Shimla

FRI, Dehradun

CSWCRTI, Dehradun

AFRI, Jodhpur

TFRI, Jabalpur

CFRHRD, Chhindwara

IFGTB, Coimbatore

RFRI, Jorhat

ARCBR, Aizawl

CSFER, Allahabad

FRC, Hyderabad

IWST, Bangalore

CSWCRTI, Kota

CSWCRTI, Bellary

CSWCRTI, Udagamandalam

CSWCRTI, Vasad

CSWCRTI, Agra

CSWCRTI, Chandigarh

CSWCRTI, Datia

CSWCRTI, Koraput

NIH, Roorkee

NIH, Belgaum

NIH, Patna

IFP, Ranchi

NIH, Kakinada

NIH, Sagar

NIH, Guwahati

NIH, Jammu

NIH & its Centres

ICFRE & its Centres

CSWCRTI & its Centres

MAP NOT TO SCALE

17

Central Soil & Water Conservation Research & Training Institute (CSWCRTI), with

headquarters at Dehradun and its eight research centres located at Agra (U.P.), Bellari

(Karnataka), Chandigarh, Datia (M.P.), Kota (Rajasthan), Koraput (Orissa),

Udhagamandalam (T.N.), and Vasad (Gujarat) are engaged in undertaking research studies in

soil and water management and hydrology aspects under all primary production systems;

developing strategies for controlling land degradation; and rehabilitation of degraded lands in

different agro-ecological zones of the country.

Indian Council of Forestry Research and Education (ICFRE), an autonomous body under

MOEF, GOI, is the apex body in the national forestry research system. The ICFRE, with its

headquarters at Dehradun, has eight Regional Institutes located at Dehradun, Shimla, Ranchi,

Jorhat, Jabalpur, Jodhpur, Bangalore and Coimbatore and four Research Centres at

Allahabad, Chhindwara and Hyderabad, etc. ICFRE is striving for the holistic development

of forestry research at national level through planning, promoting, conducting and

coordinating research, education and extension on all aspects of forestry for ensuring

scientific management of forests, improvement in forest productivity through genetic and

biotechnological researches, bioremediation of degraded land, efficient utilization of forest

products, conservation of biodiversity and integrated management of pests & diseases of

forests.

The detailed cost of the individual projects may vary depending on the site conditions,

objectives, instrumentation required, duration of the project, involvement of experts and

infrastructure required.

(iii) The committee also endorses for initiating an All India coordinated research project in

forest hydrology. A project proposal for initiating such a project in different forest types in

various geo-ecological regions may be jointly prepared by NIH, CSWCRTI and ICFRE for

funding from MOeF. The research centers of these organizations would also be involved in

implementing the projects. The proposal should include relevant review of literature, well

defined objectives, expected output, linkages, budget requirement and year wise activity

chart. Since it will be a huge task, it is recommended that based on the strength of individual

organization, the role and responsibilities of each partnering organization may be clearly

defined in the project proposal along with their budgetary requirement. The sanctioned

18

budget of each organization may be transferred to respective organization for smooth conduct

of the research components proposed by individual organizations.

7. CAPACITY BUILDING IN THE AREA OF FOREST HYDROLOGY

The research needs for advancing forest hydrology science include understanding long-

term and landscape-scale hydrologic effects of forests and the cumulative watershed effects.

Hydrologists use hydrological modelling techniques to predict water quantity and quality in

catchments where there are no measured records. Most hydrological models are developed

and tested for gauged basins and subsequently are validated and applied to un-gauged areas.

However, models that have been fitted to data in small, gauged watersheds often provide

inaccurate or imprecise predictions when they are (1) extrapolated to other small forested

headwater basins, (2) extrapolated to future time periods, or (3) applied to large catchments.

This problem of prediction in un-gauged basins has preoccupied hydrology researchers for

several decades, and is compounded by a lack of information about how direct hydrologic

effects interact under the multiple sets of specific conditions that occur in changing forest

landscapes. Spatially explicit assessments and physically based models designed to simulate,

predict, or represent these phenomena form the basic needs of forest hydrology related

models for today and the foreseeable future.

In forest hydrology, several hydrologic models have been developed for many

different objectives including prediction of the hydrologic impacts of wild fires and land use

change over different spatial scales and time periods. These models vary in how they

represent hydrologic processes linked with vegetation characteristics, soils, groundwater, and

runoff; they also vary in the spatial and temporal scales at which they simulate hydrologic

processes. However, uncertainties in landscape properties and climate inputs, choice of model

structure, and methods of information transfer from gauged to un-gauged watersheds make

the modelling task a very complicated phenomenon. In India, the science of forest hydrology

is still in infant stage and the use of forest-specific hydrological models is very uncommon.

The studies conducted so far in forest hydrology rely on the analysis of observed data from

plot scale or small watershed scale to quantify hydrological processes and the stream flows.

Sporadically, the general hydrological models have been only fitted to observed data but

19

these models do not consider forests-specific processes to account for any change in forest

characteristics. Therefore, for the advancement of the forest hydrology research in India, the

capacity building is required for the scientists to understand and use the advanced models,

developed by academicians and researchers abroad, to simulate the effect of various kinds of

changes in forests on hydrologic processes across large watersheds and on water output.

These capacity building and man power development activities can be achieved by arranging

trainings for the scientists at the organizations engaged in the development of the advanced

models of forest hydrology in countries like USA, Australia and other European countries.

20

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ACKNOWLEDGEMENTS

The committee members thankfully acknowledge the guidance and support provided by

the Director General, ICFRE, Dehradun in bringing out the report. The committee also

express sincere thanks to the Director, FRI, Dehradun and the Secretary, ICFRE Dehradun

for extending the help, logistic support and facilities during the course of committee meetings

and preparation of the report. The committee members are also grateful to the Director, NIH

Roorkee and the Director, CSWCRTI Dehradun for sparing their scientists to work in the

committee and extending all cooperation during completion of the report. Thanks are also due

to all those who directly or indirectly helped the committee in completing the task.

25

APPENDIX 1

26

27

APPENDIX 2

Modified Constitution of the Committee Based on the Suggestions of the

Committee Members in the First Meeting Held on August 11, 2011

As per Office order no. 31-19/2001-ICFRE dated 8th

July, 2011

1. Dr. K.D. Sharma

Technical Expert, National Rainfed Area Authority (NRAA),

Planning Commission, New Delhi

Chairman

2. Dr. Jaivir Tyagi (Nominee of Director, NIH)

Scientist ‘F’, National Institute of Hydrology, Roorkee

Member-Secretary

3. Dr. Laxmi Rawat

Head, Ecology & Environment Division, FRI, Dehradun

Member

4. Dr. A.K. Raina

Head, Forest Soil & Land Reclamation Division, FRI,

Dehradun

Member

5. Dr. S.P.S. Rawat

ADG (M&E), ICFRE, Dehradun

Member

6. Dr. Renu Singh

Head, Biodiversity & Climate Change Division, ICFRE,

Dehradun

Member

Following two members were included in the above committee based on the

recommendation made by the committee members during first meeting held on

August 11, 2011.

7. Dr. K.P.Tripathi (Nominee of Director, CSWCRTI)

Principal Scientist

Central Soil and Water Conservation Research and Training

Institute, Dehradun

Member

8. Dr. M.K. Gupta

Scientist E, Forest Soil & Land Reclamation Division, FRI,

Dehradun.

Member

28

APPENDIX 3

MINUTES OF THE FIRST MEETING OF THE COMMITTEE HELD ON

11 AUGUST 2011 AT NRAA, NEW DELHI TO IDENTIFY THE AREAS OF

RESEARCH AND SUGGEST MEASURES TO ACHIEVE THE MANDATE ON

FOREST HYDROLOGY

The first meeting of the committee was held in the office of Dr. K.D. Sharma,

chairman of the committee at 2.30 P.M. on 11.08.2011 in New Delhi. The Director, NIH vide

his letter no. 15/18/2011-NIH/Dir/Nomi, dated 25 July 2011 nominated Dr. Jaivir Tyagi,

Scientist ‘F’ as representative of NIH in the above committee. The following members were

present in the meeting.

1. Dr. K.D. Sharma

Technical Expert, NRAA, New Delhi

Chairman

2. Dr. A.K. Raina

Head, Forest Soil & Land Reclamation Division, FRI, Dehradun

Member

3. Dr. S.P.S. Rawat

ADG (M&E), ICFRE, Dehradun

Member

4. Dr. Jaivir Tyagi

Scientist ‘F’, NIH Roorkee

Member

Dr. Laxmi Rawat and Dr. Renu Singh could not attend the meeting due to

preoccupation.

At the outset, the chairman welcomed the members of the committee and briefed

about the background and mandate of the committee. He then invited the members to suggest

the research issues in the area of forest hydrology and the roadmap to achieve the goal. A

detailed discussion was held on various research issues related to forest hydrology in the

context of Climate Change. After thorough deliberations by the members, the following

actionable points were agreed upon:

1. Dr. Jaivir Tyagi, Scientist ‘F’ was nominated as Member-Secretary of the committee.

2. The Member-Secretary was entrusted with the work of preparation of the draft report

based on the inputs received from other members of the committee.

29

3. Dr. A.K. Raina would provide the write up on various soil properties including physical,

hydrological, chemical, geological and mineralogical, in different forested regions of

India which have significant impact on water quantity and quality generated from the

forested lands.

4. Dr. S.P.S. Rawat would provide the write up on suggested measures/roadmap to achieve

the research mandate proposed by the committee.

5. In view of the additional specific inputs needed for preparation of draft report, the

present committee needs to be expanded to include the following experts:

(i) Director, Central Soil & Water Conservation Research & Training Institute

(CSWCRTI) Dehradun or his representative.

(ii) Dr. M.K. Gupta, Scientist E, Forest Soil & Land Reclamation Division, FRI,

Dehradun.

6. The CSWCRTI would provide the write up on present status of research on forest

hydrology and the research gaps.

7. Dr. M.K. Gupta would provide the details on the role of forests on carbon sequestration

and its impact, if any, on hydrological regime of forested watersheds.

8. The members would provide the inputs as decided in the meeting to the Member-

Secretary through email by the end of August 2011.

9. The following broad areas of research on forest hydrology in the context of climate

change were tentatively identified by the committee:

(i) Compilation of status of research on forest hydrology in India and abroad.

(ii) Preparation of a catalogue of historical and modern hydrologic records

(iii) Continuing current small watershed experiments and re-establishing small

watershed experiments where research has been discontinued

(iv) Selection of paired representative watersheds (two watersheds similar in size,

initial land cover and other attributes) in different geo-ecological conditions for

long term hydrological measurement using an integrated approach of hydrologic

instrumentation, field investigation, remote sensing and GIS techniques. One

watershed may be kept as control while other may be treated subject to

manipulations such as change in forest cover and forest management practices.

30

(v) Monitoring water quality parameters of streams and springs in the selected

representative watersheds

(vi) Effect of global warming and climate change on migration of forest types with

respect to altitude, changes in structure and composition of forests and the effects

thereof on the hydrological parameters including ET and runoff.

(vii) Hydrological investigations on the effects of different tree species and forest types

on interception, infiltration, soil moisture, ET, water yield and groundwater

(viii) Effect of different forest management practices on water yield, flood peaks,

regulation of stream flows, sediment yield, water quality, etc.

(ix) Monitoring of spring discharge which represents the groundwater in the forested

mountainous watersheds.

(x) Investigations on changes in soil physical properties, moisture holding capacity of

soils and carbon sequestration under different forest species.

(xi) Besides above, any other pertinent research topics may also be suggested by the

members for inclusion in the draft report and may be communicated to Member-

Secretary along with brief write up.

10. The next meeting of the committee will be held in the third week of September at FRI,

Dehradun to finalize the draft report.

At the end, the chairman thanked the members of the committee. The committee

members also expressed thanks to the chair.

31

APPENDIX 4

32

APPENDIX 5

33

Annexure 1

Reviews on Status of Research in Forest Hydrology in India

K.P.Tripathi1, D.R.Sena

2 and G.P.Juyal

3

1Principal Scientist

2Senior scientist (Soil and Water Conservation Engineering)

3Head (Division of Hydrology and Engineering)

Central Soil & Water Conservation Research & Training Institute, Dehradun

Forest hydrology deals with the role of forest over precipitation (loosely rainfall) and

Water yield (loosely runoff) generating potential of the forest in conjunction with other

parameters namely soil, topography, vegetation management and land management

practices. The runoff resulting from rainfall is paramount importance to all living on this

earth. The runoff can be manipulated by modifying the parameters influencing it. The runoff

is a function of rainfall, soil, topography, vegetation and its management, and land

management practices

Forestry is the science that seeks to understand the nature of forests and the

interactions between the parts comprising a forest.

Hydrology is the science that studies the waters of earth. Hydrology seeks to

understand where water occurs; how water circulates; how and why water distribution

changes over time; the chemical and physical properties of water; and the relation of water to

living organisms. The water goes through various forms of transformation from one kind to

another. The main source of water for all of us in the sea and which roughly occupies about

70 percent of the total area of the earth. The relationship of rainfall and run off is explained

by hydrological cycle.

The hydrologic cycle, also known as the water cycle, describes the continuous

movement of water on, above and below the surface of the earth. Since the water cycle is

truly a "cycle," there is no beginning or end. Water can change states among liquid (rain),

vapour (evaporation and transpiration), and solid (ice) at various places in the water cycle.

Although the balance of water on earth remains fairly constant over time, individual water

molecules can come and go. Over geological time, water-rich planets such as the earth lose

gases such as hydrogen over time, which can lead to run away greenhouse effects which in

turn accelerate hydrogen loss, and by association water loss, from a planet's atmosphere.

Principles of hydrologic response to changes in forest structure:

1. Partial or complete removal of the forest canopy decreases interception (precipitation

captured by leaves and branches) and increases net precipitation arriving at the soil

surface.

2. Partial or complete removal of the forest canopy reduces transpiration (water lost from plants to the atmosphere).

3. Reductions in interception and transpiration increase soil moisture, water availability to plants, and water yield.

34

4. Increased soil moisture and loss of root strength reduces slope stability. 5. Increases in water yield after forest harvesting are transitory and decrease over time as

forests re-grow.

6. When forests of high interception (or higher annual transpiration losses) replace forests with lower interception (lower transpiration losses), this change reduces water

yield as the new forest grows to maturity.

Principles for changes in water flow paths in soils and sub soils:

1. Impervious surfaces (roads and trails) and altered hill slope contours (cut slopes and fill slopes) modify water flow paths, increase overland flow, and deliver overland

flow directly to stream channels.

2. Impervious surfaces increase surface erosion. 3. Altered hill slope contours and modified water flow paths along roads increase

landslides.

Principles of hydrologic response to applications of chemicals:

1. Forest chemicals can adversely affect aquatic ecosystems especially if they are applied directly to water bodies or wet soils.

2. Forest chemicals (fertilizers, herbicides, insecticides, fire retardants) affect water quality based on the type of chemical, its toxicity, rates of movement, and

persistence in soil and water.

3. Chronic applications of chemicals through atmospheric deposition of nitrogen and sulfur acidify forest soils, deplete soil nutrients, adversely affect forest health, and

degrade water quality with potentially toxic effects on aquatic organisms.

The influence of forests on their environment forms part of a complex relationship

between environment and forest. Investigators have investigated for past several decades to

ascertain the influences of forests on hydrological parameters and water availability. In this

direction, forest influences on various hydrological parameters viz. rainfall, interception,

infiltration, soil moisture, evapotranspiration, groundwater, water yield, soil loss and floods

etc. forms an important area of hydrological studies. A summary of results of studies done in

this regard in the country and elsewhere is given in following sections.

Rainfall

In India, limited studies have been directed towards the effects of forests on rainfall.

In 1906, a committee was set-up by Govt. of India to find the relationship among forests,

atmosphere and soil; which concluded that the effects of forest on rainfall were probably

small (Hill, 1.916). Voeleker (Lohani, 1985) had conducted studies on small plots for about

52 years on rainfall and forest data in Nilgiris and had concluded that the planting of trees

increased the number of rainy days on local scale. Another study indicated that there was no

increase in rainy days during monsoon period (Ranganathan, 1948). Bhattacharya (1956)

after conducting intensive studies in Pathri, Ranipur and Ratmau (in U.P. hills) concluded

that planned deforestation did not have any effect on rainfall. Pisharoty opined that local

changes due to deforestation are less likely to affect the meteorological aspects and quoted

experiments done in Germany and England in support of his opinion (quoted from Mistry,

1987). Biswas (1980) has related percentage of forest cover with total rainfall in A&N Group

35

of Islands and concluded that rainfall seems to increase with forest cover. However, India

Meteorological Department (IMD) denies any correlation between deforestation and rainfall

(Agarwal et. aI. 1987). In a detailed study conducted in Western Karnataka and part of

Kerala. Mehar Homji (1986) concluded that forest clearance did not seem to reduce the total

number of rainys days. Dutt and Manikiam (1987) have concluded based on results of several

studies that deforestation has effects on rainfall on local scale but on regional or global scales

these effects are not significant. Gupta et al. (2005) based on simulation model using T42

version of CCM3 with a horizontal resolution of 2.8o X 2.8o that for 100% deforestation

there will be change in spatial distribution of rain rate in India i.e. Northern part of India, rain

rate is expected to decrease upto 2 mm/day where as over southern part of India, including

Arabian Sea and Bay of Bengal the rain rate will increase up to 5 mm/day. In north eastern

part of India there will be decrease in rainfall about 4 mm/day. However this study is the case

due to large scale deforestation.

Based on the limited studies done in India it may be concluded that the results are

generally inconclusive in nature, indicating that forests and rainfall relationship are not

monotonic on a regional scale. However, in coastal forests the precipitation may be more

because of interception and then condensation of fog by forests.

Interception

The results obtained in various interception studies carried out in India and abroad by

Dabral et. al. (1963), Dabral and Subbarao (1969), Mathur et. al. (1975), Lull (1964) and

others (as given in Appendix-I) indicate that the canopy interception varies from 15% to 35%

of rainfall for different species of forests. There is evidence that interception varies not only

with type of species, canopy density etc. but also with intensity of rainfall, as is evident from

Table 1 & 2 (Mathur et.al., 1975). It indicates that interception reduces with increase in

rainfall amount and beyond 60 mm rainfall/storm; the interception loss reduces to

significantly low values.

It can be concluded that the interception is a function of forest type. density,

composition, structure and rainfall amount/intensity. Partial or complete removal of the

forest canopy decreases interception (precipitation captured by leaves and branches) and

increases net precipitation arriving at the soil surface It may be inferred that the average

total interception by a dense forest cover (including canopy interception 20%, undergrowth

10% and litter interception 5%) appears to be around 35%. It has also been observed that

the interception is higher from needle leaved trees as compared to broad leaved trees. The

interception in forested catchments does not have significant effect during heavy storm (100

mm or so). However, this is important from soil conservation view point.

Infiltration

Results obtained from some studies done in the country and abroad regarding

infiltration rates under various land uses are presented in Table 3. I n a study conducted at

Bellary (semi-arid region) and Ootacamund (Nilgiri hills) under different vegetative covers,

the results indicated maximum infiltration rates for woodlands as 17 cm/hr and for Shola

forest (miscellaneous vegetation) as 12.5 - 16.8 cm/hr. In Bihar, Mistry and Chatterjee (1965)

recorded average infiltration rates as 26, 12 and 9 cm/hr under forests grasslands and crop

lands, respectively. A comparative study of infiltration rates conducted in Dehradun (North-

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Western Himalayan region) under Eucalyptus, Sal, Chir, Teak, Bamboo and grassland gave

initial infiltration rates as 54.0, 21.4, 12.0, 9.6, 9.6 and 7.6 cm/hr, respectively. In the same

study,. effects of fire on infiltration in Chirr plantation was studied and infiltration was found

to reduce to a value of 3.6 cm/hr. The analysis of infiltration data from small forests and

agriculture watershed in Doon valley indicated that the rate of infiltration was twice in forest

watershed (Shorea Robusta) as compared to agriculture watershed (Dhruvanayayana and

Shastri (1983). A study in Sainji, a forest watershed of Himalaya suggests that old oak forest

(with humus content more than 3% with top 10 to 12 cm of humus content) infiltration rate is

as high as 159.48 cm/h comparison to young oak forest which has 36.55 cm/h. A scrub forest

with biotic activities has infiltration rate as low as 6.25 cm/h (Sena et al., 2011). This is due

to a complex combination of infiltration, infiltration and macro flow phenomenon

In general, it can be inferred d that the infiltration rates are relatively more in

forested soils as compared to agricultural areas & grasslands. Based on the results of some

of the infiltration studies carried out, it could be inferred that infiltration rates from arable

crop land and grasslands are nearly 30 to 35% and 40-50%, respectively of that from forest

lands. However, it is drastically affected due to biotic interferences like forest fires tampling

by cattles, removal of leaf litter etc.

Soil Moisture

A limited number of studies have been conducted to observe the effects of forest on

soil moisture regime. In a study conducted at Dehradun, it has been observed that soil

moisture (in mm of soil depth) remains at higher level under forest than grass, e.g. bamboo

(14-102%), teak (30-73%). Results of soil moisture studies conducted in Nilgiris in latritic

soil under various land uses are given in Table 4. It can be observed that soil moisture always

remains' higher in forested lands as compared to agricultural lands.

In general, it can be concluded that much efforts have not been made to quantify soil-

moisture storages under forests. However, forested soils have a better soil moisture retention

capacity due to improved soil structure because of more humus and organic content.

Evapotranspiration

As for the effects of forests on evaporation, the presence of forests may provide shade to

ground, thereby reducing both air and soil temperatures and also wind velocity which finally

reduces evaporation. One of the measures to reduce reservoir evaporation is by growing thick

forest along the periphery of the reservoir. As a result the wind velocity at the reservoir

surface gets reduced which reduces evaporation from reservoirs. The presence of forests also

affects temperature in terms of having effects on surface albedo. As stated by Pereria (1973)

the reflection ranges from 12% for pine forest to 40% for deserts. Obviously lower the albedo

and more will be the energy available for evaporation losses in case of forested area.

Studies leading to computation of forest transpiration have indicated that forests

generally absorb more radiant energy which is available for transpiration. A limited number

of studies done, have indicated that forests have generally high evapotranspiration (ET)

requirement as compared to other land uses. Results of few such studies have been

summarized in Table 5. Gupta (undated) has cited Engler's observation as the. transpiration of

forest compared with crop land and meadows could be indicated as 100: 43 : 22.

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The studies conducted in India and abroad indicate that forests have higher ET

requirements as compared to other land uses. However, more studies are required to be done

for systematic computation of ET by forests.

Groundwater

There exists limited information in Indian context that corroborates the relationship of

forest in augmenting groundwater recharge. In the studies conducted for Nilgiris in India,

Samraj (1984) observed that plantation of Eucalyptus tree has resulted in significant lowering

of base flows.

The effects of forests on groundwater have not been studied on large scale. A limited

number of studies have indicated non-coherent results.

Water Yield

The availability and quality of water in many regions of the world are more and more

threatened by overuse, misuse and pollution, and it is increasingly recognized that climate

change is altering forest’s role in regulating water flows and influencing the availability of

water resources. Therefore, the relationship between forests and water is critical issue that

must be accorded highest priority.

Trees through their root system allow a definite volume of percolation and subsequent

movement of percolated water. The roots also extract soil moisture regularly to provide

necessary nutrients to super-structure above the ground. Thus, when forest is cut, this system

gets snapped all of a sudden and thereby water gets stored into the soil profile and its

subsequent utilisation or deposition by plant body gets disturbed. This results in sudden

increase in water yield in the form of surface runoff. The results of experimental studies

conducted in USA and elsewhere have shown increased stream flow following forest cutting

in a watershed. In Japan and Kenya also a large increase in water yield was observed

following clearing of forests (Hibbert, 1965). It has also been observed at places that

removing 30% or less of the forest cover would not produce a significant change in stream-

flow. In India, Subbarao et. al (1985) did not record any significant increase in fortnightly

water yield after imposing 20% of forest thinning in coppice sal forest at Dehradun. It has

also been observed that reforestation of a small brushwood watershed (1.45 ha) by

Eucalyptus species (replacing brushwood) reduced water yield by 28%. Results of some such

studies under Indian condition are summarized in Table 6.

Based on studies reported above, it can be inferred that substantial reduction of

densities of forest overstories and thinning (more than 30%) increase water yield and

establishment of forest over-storey on sparsely vegetated land and/or changing to fast

growing species like Eucalyptus decrease water yield. This decrease is more significant in

first few years of growth. Besides, the type of land cover, the size of watershed have also

important bearing on water yield. Based on various studies, it appears that in small

watersheds forests tend to decrease the water yield (i.e. due to decreased surface runoff)

while in large watersheds, the subsurface component of total water yield (delayed yield) gets

increased.

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Eucalyptus (Bluegum) plantation and Water Yield

The hydrological behaviour of small identical watersheds; one with natural grassland

and “shola” forest and the other with Eucalyptus globulus (bluegum) plantation was studied

from 1968 to 1992 following the paired watershed technique in the Niligris in Western Ghats

of South India. Following the calibration period from 1968-1971, bluegum plantation was

raised in 59 per cent area of a watershed above the frost lien during 1972 and it was felled

after first rotation of 10 years and subsequently after another 10 years rotation of the

coppiced bluegum. Regression and double mass curve techniques were employed to analyze

stream flow data to determine changes in water yields. Flow duration curves and Low Flow

Index (LFI) were used to quantify the effect of bluegum on low flow regime. Effect of

bluegum on high flows was investigated using simple ratios, regression analysis, cumulative

frequency plots and probability analysis. Growth parameters of grassland and bluegum

plantation were also studied.

The study area is located at Glenmorgan (latitude 11°28’10” N and longitude

76°37’14”E), 24 km away from Udhagamandalam on Udhagamandalam Mysore road in

Wenlock Downs Forest Reserves in the Nilgiris district of Tamil Nadu. The study area

consists of two small adjoining watersheds (each about 32 ha; Table 7) having nearly

identical topography, slope, vegetation and soil characteristics. It falls in the catchment of

Glenmorgan storage reservoir feeding the Pykara hydro-electric project in Moyar basin.

The bluegum plantation was spread over an area of 18.76 ha out of 26.8 ha of

grassland and possessed 20463 marketable bluegum trees in addition to a few Acacia trees

which invaded into the bluegum coppiced plantation. The wood biomass production for the

second rotation was 14.1 t/ha/yr as against 10 t/ha/yr (1972-1981) during the first rotation,

registering an increase of 41 per cent in wood biomass.

Conversion of natural grassland into bluegum plantation reduced seasonal and annual

water yields, decreased low flow as well as decreased peak flows and increased soil moisture

losses. These effects were more pronounced during the second rotation (i.e. First coppiced

growth) as compared to the first rotation. Average annual reduction in water yield of the

order of 16% and 25.4% was determined from the bluegum watershed over the natural

grassland during the first and second rotation, respectively (Table 8). Maximum reductions in

runoff were observed during the winter, summer and pre-monsoon seasons. Significant

reduction in low flows as a result of decline in base flow could be predicted with Low Flow

Index (LFI) decreasing by 2.0 and 3.75 times, in the first and second rotation respectively.

Moderation in peak discharge rates was also observed as a result of bluegum plantation. A

sudden increase in runoff immediately after the coppicing of bluegum lasted for about one

year. The wood biomass for the second rotation was also 41 per cent higher than the first

rotation. These results clearly suggest that hydrological caution may have to be exercised

while planning large scale conversion of natural grasslands into bluegum plantations in the

catchments of hydel projects in the Nilgiris.

There was an increase in annual flow (14 to 17%) immediately after felling of

bluegum trees at the end of first and second rotation. Hydrologic recovery was very fast and

this increase lasted for a short duration of about one year. Significant difference (reduction)

in soil profile moisture at 0.5 m to 1.0 m depths was observed during the second rotation of

10 years of bluegum watershed over the grassland and this reduction was more than that of

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first rotation of 10 years. During second rotation bluegum appears to have extracted moisture

from 1.0 m soil depth as the roots penetrated upto 3.2 m.

Increases in water yield after forest harvesting are transitory and decrease over time

as forests regrow.

Water yield from various watersheds at Almas (Tehri, Uttarakhand)

The annual runoff (%) as that of annual rainfall from three nested watersheds of (i)

535 ha mixed with Forest, Grassland and Agriculture, (ii) 105 ha with mixed Forest, and (iii)

267.5 ha with oak forest located at Almas watershed (Tahsil: Dhanulti; District : Tehri; State:

Uttarakhand) was measured with the help of rectangular/ trapezoidal weir with the help of

mechanical water level recorder from 2001 to 2009.Water yield from the 535 ha watershed

varied from 0.70 percent to 22.6 percent as that of annual rainfall. The water yield from

nested bouldry watershed of 105 varied from nil to 11.3 percent. The thick oak forest of

267.5 ha recorded water yield of 7.5 % to 41.3 % m recoded during 2008 (Table 9). The

variation was mainly due to the rainfall characteristics of each year, diversion of water by 65

mm underground pipe line for irrigation during long spell between two successive storms

(Anonymous, Annual Report, CSWCRTI Dehradun, 2000-2010; Tripathi et.al.).

Water yield from various watersheds at Sainji (Tehri, Uttarakhand)

The impact of various conservation measures on flow behaviour of three micro

watersheds was analysed by dividing the entire data set of 09 year (2001-2010) into two

blocks covering treatment period (2001-02 to 2003-04) and post treatment period (2004-05 to

2009-10). Trends of flow during 2001-02 to 2003-04 in the main watershed (WS1), scrub

forest watershed (WS2) and oak forest watershed (WS3) reveal that the average surface runoff

in WS1, WS2 and WS3 was 3, 4.8 and 2.4% of total rainfall, while the corresponding values of